Question

For my university project, I’m developing a dynamic live chat website with rooms, user registration, etc. I’ve got the entire system planned out bar one aspect. The rooms.

A room is created by a user who is then an operator of that room. Users can join the room and talk within it. The system has to be scalable, accounting for hundreds of thousands if not millions of messages being sent a day.

I was going to create on table in my database called messages, and have fields like this:

| r_id | u_id | message | timestamp |

r_id and u_id would be foreign keys to the room ID and user ID respectively. This would mean I would insert a new record when a user sends a message, and periodically run a SELECT statement for every client (say every 3 seconds or so) to get the recent messages. But because the table will be huge, running these statements might create a lot of overhead and take a long time.

Another way of implementing this would be to create a new database table for every room. Say a user creates 3 rooms called General, Programming and Gaming. The database tables would be room_general, room_programming, and room_gaming, each with fields like:

| u_id | message | timestamp |

This would drastically cut down on the amount of queries for each table, but might introduce problems when I come to program it.

So, what is the best way to do this?

I’m using MySQL with PHP and AJAX.

Answer 1

It is bad idea to create a table per room. Hard to implement and hard to support.

Dont worry about performance of selects because they will be wery simple:

SELECT * FROM messages WHERE r_id=X ORDER BY timestamp DESC LIMIT X,Y

Just make sure your (r_id, timestamp) indexed together in this order to make this select using index:

ALTER TABLE `messages` ADD KEY `IN_messages_room_time` (`r_id`, `timestamp`);

If you will still have problems with performance (probably you will not), just add a 1-3 seconds inmemory cache (using memcache) and fetch a messages from DB one time per 1-3 seconds.

Also look at the Apollo Clark’s answer: https://stackoverflow.com/a/8673165/436932 to prevent storing huge amount of unneccessary old messages: you can just put it in to the MYISAM table archive or simply delete.